Spatial transverse single-mode and multi-mode structures have been known as structures of conventional semiconductor laser devices. Among these, with a single-mode type semiconductor laser device, a waveguide is formed to be narrow in width to restrict the oscillation mode within the waveguide to a single-mode. However, when the width of the waveguide is narrow, an emission end is also made small in area. Also, when the laser light density at the emission end is excessive, the reliability, etc., of the semiconductor laser device are affected. Single-mode type semiconductor laser devices are thus favorably employed in applications using laser light of comparatively low output. As an example of a single-mode type semiconductor laser device, there is the semiconductor laser apparatus disclosed in Patent Document 1. With this semiconductor laser apparatus, the width of a waveguide in a single-mode type semiconductor laser is expanded to increase the laser light intensity.
Meanwhile, with a multi-mode type semiconductor laser device, because a plurality of modes may coexist inside a waveguide, the waveguide can be formed to be wide in width. An emission end can thus be made large in area and laser light of comparatively high intensity can be emitted. Such multi-mode type semiconductor laser devices are favorably employed in applications requiring laser light of comparatively high output.
However, multi-mode type semiconductor laser devices have the following problems. That is, because a plurality of modes coexist inside the waveguide, the emission pattern of a laser light emitted from the emission end is disordered and the emission angle is comparatively large. A lens for converging or collimating this laser light thus becomes complex in shape, and there may be thus the demerit that the desired laser light may not be obtained or the lens is expensive.
As an art for resolving the above problem of multi-mode semiconductor laser devices, there is, for example, the resonator disclosed in Patent Document 2. FIG. 23(a) is a plan view of an arrangement of this resonator. This resonator 100 has two regions 102a and 102b inside an active layer 101. FIG. 23(b) is a diagram of a refractive index distribution in a section taken on line VII-VII or line VIII-VIII of FIG. 23(a). As shown in FIG. 23(b), the refractive index n2 of the regions 102a and 102b is less than the refractive index n1 of other regions of the active layer 101. Also, the regions 102a and 102b are formed inside the active layer 101 at an angle at which a light L, reflected perpendicularly at an emission end 100a and a reflecting end 100b, is totally reflected by side surfaces of the regions 102a and 102b. In the Patent Document 2, this arrangement is used to restrict the optical paths of the light L that resonates inside the active layer 101 to realize single-mode oscillation without restricting the waveguide width.
Patent Document 1: Japanese Patent Application Laid-Open No. H10-41582
Patent Document 2: International Patent Publication Pamphlet No. 00/48277